St. Roswald, Celestial Dragon

St. Roswald, Celestial Dragon cannot block.
When St. Roswald, Celestial Dragon dies, it's
controller may search their deck for a legendary
Marine creature card and put it onto the battlefield as a face down enchantment with
"Turn this card face up for {r/w}{r/w}{r/w}".
If a source an opponent controls killed St.
Roswald, that player gains life equal to the
excess damage.